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New Scientist Live

Polar bears shift from seals to bird eggs as Arctic ice melts

Poaching eggs

Jouke Prop

By Thom Hoffman

Polar bears are ditching seafood in favour of scrambled eggs, as the heat rises in the Arctic melting the sea ice. A changing coastline has made it harder for the predators to catch the seals they favour and is pushing them towards poaching goose eggs.

This is according to a team led by Charmain Hamilton of the Norwegian Polar Institute that monitored the movements of local polar bears and seals before and after a sudden decline in sea ice in 2006, which altered coastal areas in the Norwegian archipelago of Svalbard.

The researchers attached tracking devices to 60 ringed seals and 67 polar bears overall, which allowed them to compare their movements before and after the ice collapse.

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Before the melt, when they were hunting on stable sea ice, the polar bears had a big advantage over their favoured prey. “Both sexes of all age classes successfully hunt seals by stalking or ‘still hunting’,” says Hamilton.

However, on a melting coastline punctuated by broken-up icebergs, the odds become stacked in the seal’s favour.

In deep water

The polar bears must now swim undetected towards the seals before launching themselves out of the water to grab their prey on the floating chunks of ice. Not all bears have mastered this explosive technique and there is a high failure rate even among those that have.

“It seems that currently, it is mainly large, male bears using this aquatic hunting method on Svalbard,” says Hamilton. “It is likely [to be] more energetically demanding than the traditional hunting methods.”

Rare success at seal hunting

Kit Kovacs/Christian Lydersen, Norwegian Polar Institute

In response, the bears are retreating from the coast. The tracking devices show them wandering greater distances in search of alternative land-based food. The bears also spend a lot more time near bird nesting grounds, which suggests eggs have become a significant food source.

But they would need an immense omelette to replace a seal breakfast and this type of mass egg hunting can devastate nesting bird populations.

Ecologist Jouke Prop at the University of Groningen, Netherlands, is also studying geese in the Arctic. He has filmed bears devouring goose eggs at nesting sites.

Smash and grab

“It takes on average 30 seconds to locate a nest and 60 seconds to eat the eggs,” he says. Previous research found that affected bird populations can slump by up to 90 per cent.

“It is extremely intriguing how the habit of bird egg eating is developing within the polar bear population,” says Prop. “Which bears are eating eggs? Did they learn from their mothers?”

“I have seen the diarrhoea faeces of bears eating eggs,” says Maarten Loonen at the University of Groningen. “I think eggs are not their best favourite food. Too much protein. Nevertheless, they have to eat something and they probably can survive on it.”

The bears seem to be getting enough nutrition to survive, but Hamilton wonders what the long-term effects of this change in diet will be. “Seal fat is an extraordinarily rich source of lipids that will be very hard to replace,” she says.

As the bears move on to eating bird eggs for sustenance, what will happen to the geese population in the future?

“If numbers decline – which is to be expected – this will have an impact on the whole terrestrial ecosystem,” says Prop. “For example, Arctic foxes depend on young geese as food; reindeer food intake is facilitated by geese grazing the tundra.”